1. Field of the Invention
The present invention relates to a resistance welding apparatus and method for stabilizing the welding quality in resistance welding such as spot welding.
2. Background Art
It is known that a preset welding current Iw is kept flowing for a preset energizing time T despite spattering during passage of a welding current as shown in FIG. 8(a). In addition, there is known a spot welding method in which the welding current at a beginning of the welding is set to a current value in an expulsion (spattering) occurring region and the current value is reduced to 0.5 to 0.9 times the original value at the time point the expulsion has occurred and the resulting current is supplied at least for three cycles (for example, refer to JP-A-61-014089).
In case spatters are generated, a nugget size is reduced and a nugget growth speed drops by generation of the spatters as shown in FIG. 8(b) even when the preset welding current Iw is kept flowing for a preset energizing time T. Thus, the required nugget size may not be reached and the strength may be insufficient.
The spot welding method disclosed in JP-A-61-014089 has a problem of extended cycle time.